Cold shrink (CS) splices are used to achieve a tight fit around cables and bundle cables together for protection against environmental factors. A conventional CS product typically comprises a flexible tube of an elastomer, which is held in expanded condition on a support core designed for removal from inside the flexible tube. During installation, the supporting core collapses on demand to allow the tube to shrink into contact with a wire or cable that needs protecting. Therefore, compared to the traditional heat shrink and pre-molded technology, the cold shrink splices have several advantages such as ease and repeatability of installation (no heat, no tools required) and broader cable size accommodation (reduced part inventory).
Since a sufficient shrink/retract from the expanded condition to original condition is needed, there is a high requirement on the tensile recovery performance, i.e., a low tensile permanent set is required.
Current cold shrink products in the market are made of silicon rubber such as high temperature vulcanization (HTV) and liquid silicone rubber (LSR), which have excellent tensile recovery performance due to their low inter-molecular interaction and less molecular entanglement. However, there are also several drawbacks for such silicon-rubber based CS products such as low tear resistance and low alternating current break down (ACBD) strength. The CS products may be damaged during demolding and expanding process if the tear resistance is not sufficient. In addition, end-users have reported tear failure during installation or usage. It is believed that since the part remains stretched during its service life, a low tear strength results in rapid crack propagation if initiated by a sharp object during installation or pinched form the surrounding environment during its service life. Also the high ACBD strength is a key requirement in the cable accessories application for connection longevity.
Blends of silicone rubber with a polyolefin (PO) elastomer show improved tear resistance and dielectric strength; however, the poor compatibility between PO elastomers and silicone rubber makes it difficult to attain such blends and increases costs. For example, current approaches for improving the compatibility between PO elastomers and silicone rubber focus on adding silane- or maleic anhydride (MAH) grafted PO elastomers to the PO/silicone rubber blends. Crating the functionalized polymers increases cost and production time. Furthermore, it is very difficult to graft MAH onto an unsaturated PO elastomer, such as ethylene/propylene/diene modified (EPDM) elastomers due to crosslinking side reactions.
There is a need for improved cold shrink materials having excellent tensile recovery performance as well as low tear resistance and low ACBD strength.